With direct injection diesel engines for motor vehicles, reducing NOx emissions by storage/release DeNOx catalysis is one technical solution envisaged for compliance with the standards relating to this type of pollution, and in particular the EURO IV standards.
To this end, it is envisaged to use a NOx trap adapted to absorb NOx during standard operation of the engine and consisting of barium sulfate, for example.
It is proposed to trigger a transient release stage when the trap is saturated by momentarily switching the engine from the standard mode of operation with a lean mixture to a regeneration mode of operation with a rich mixture in order to produce reducing agents, for example HC and CO, that reduce the NOx, which is then desorbed from the trap, as in a conventional catalytic converter.
However, that causes problems with stable control of the operation of the engine when using a rich mixture over the whole of its range of operation without impacting on driver comfort, combustion noise, etc.